A trans-impedance amplifier is an amplifier circuit arranged to convert a current into a voltage. The gain of a trans-impedance amplifier is the ratio of the output voltage to the input current. The magnitude of the gain provided by the trans-impedance amplifier can be controlled by a feedback resistor. In some arrangements the feedback resistor is connected between the inverting input and the output of an inverting amplifier with high input impedance. The input impedance of the inverting amplifier causes the input current to flow through the feedback resistor producing the output voltage.